#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
const int MAXN = 10007;
double p[MAXN], h[MAXN];
double ANS(int n, double d, double b) {
    double xd = d/(b+1);
    double v = 1e9;
    for (int i=0; i<n; ++i) {
        double x = p[i] - ((int)(p[i]/xd))*xd;
        double Vx = (x*xd/2 - x*x/2)/h[i];
//        printf("Vx : %lf\n", Vx);
        v = min(v, Vx);
    }
    xd /= 2;
//    printf("xd: %lf\n", xd);
    if (xd < v) v = xd; //d*d/(b+1)/(b+1)/4;
    return sqrt(v+xd*xd/v);    //d*d/(b+1)/(b+1)/4/(v));
}
int main(int argc, char** argv) {
#ifdef hai
    freopen("in.txt", "r", stdin);
#endif
    int n;
    double d,b;
    while (cin>>d>>n>>b) {
        for (int i=0; i<n; ++i) {
            scanf("%lf %lf", p+i, h+i);
        }
        double ans = 1e9;
        for (int i=b; i>=0; --i) {
            double t = ANS(n, d, i);
//            cout<<"t: "<<t<<endl;
            ans = min(ans, t);
        }
        printf("%0.5lf\n", ans);
    }
    return 0;
}
